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An effort to put light on the common health hazards caused by improper ergonomics and a glance over the proper ergonomic practises to be followed in daily dental practise to increase the ease and efficiency of your practise..
• In Greek, “Ergo,” means work and, “Nomos,” means natural laws or
• Ergonomics,therefore, is an applied science concerned with designing
products and procedures for maximum efficiency and safety.
• Ergonomics modifies tools and tasks to meet the needs of people,
rather than forcing people to accommodate the task or tool.
• Ergonomics is concerned with the
efficiency of persons in their working
• It takes account of the worker’s
capabilities and limitations to ensure
that tasks, equipment, information
and the environment suit each
worker (Kahri, 2005).
• Studies show that 1/10 dentists
report having poor general health
and 3/10 dentists report having
poor physical state (Gorter et
• Recently, “Ergonomics” has become a popular term.
• The term has been used with most professions but increasingly in the
• It is a discipline that studies workers and their relationship to their
This includes many different
concepts such as,
• how dentists position
themselves and their patients
• how they utilize equipment
• how work areas are designed
• how all of this impact the health
of dentists (Russel, 1973)
Application of Ergonomics
• Through ergonomic advances made over the years, dental
professionals have been able to modify and optimize their working
• Ergonomic improvements in seating, instrumentation, magnification,
lighting, and gloves have offered a proactive measure for ensuring a
proper balance between job requirements and worker capabilities.
• MSDs are injuries and disorders of the musculoskeletal system.
• The musculoskeletal system includes muscles, tendons, tendon
sheathes, nerves, bursa, blood vessels, joints/spinal discs, and
• Researchers have found symptoms of discomfort for dental workers
occurred in the wrists/hands (69.5%), neck (68.5%), upper back
(67.4%), low back (56.8%) and shoulders (60.0%).
Musculoskeletal disorders amongst Greek endodontists: a national questionnaire survey. Int Endod J. 2014
Aug;47(8):791-801. doi: 10.1111/iej.12219. Epub 2014 Jan 11
• MSDs were reported by 61% of the participants. Of them, 69%
reported pain to more than one body part.
• The prevalence of disorders was highest in the lower back (30%) and
• Awkward postures during practice (OR:4.561, 95% CI:1.341-15.512),
regular stretching exercises (OR:0.032, 95% CI:0.010-0.110) and
number of patients day(-1) (OR:3.524, 95% CI:1.686-18.100) were
significant predictors for MSDs.
MSDs and Endodontists
• Conditions can vary from mild recurrent symptoms to severe and
incapacitating.Early symptoms of MSDs include
• tingling sensation
• loss of strength.
• Awkward Postures
• Posture is a term used for the
position of various parts of the body
during an activity.
• For most joints, a good or “neutral”
posture means that the joints are
being used near the middle of their
full range of motion.
• For example, when arms are fully
outstretched, the elbow and shoulder
joints are at the end of their range of
• If an individual pulls or lifts repeatedly
in this position, there is a higher risk
of injury (OHSCO, 2007).
• Researchers have confirmed the presence of awkward postures
specifically in the neck, back, shoulders, hand and wrist for dental
• Awkward postures are often adopted due to improper
seating,improper patient positioning and/or poor work techniques.
• Common awkward postures in dental practice include elbow and
wrist flexion and thumb hyperextension, which have been shown to
stress neurovascular structures and ligaments.
• Static postures are defined by those which are held for a long period
of time and may result in fatigue and injury.
• Oxygen is delivered to the muscles and joints by blood.
• Researchers have found that even 30 degrees of forward shoulder
flexion or abduction can cause a significant impairment in blood
circulation within the shoulder / neck region (Jarvholm,1989).
• Furthermore, dental practitioners have been
observed statically holding postures requiring
greater than 50% of the body’s musculature to
• Static gripping for durations exceeding 20
minutes was also noted during instrumentation
tasks within dental practice (Sanders).
• Force refers to the amount of effort created by the muscles as well as
the amount of pressure placed upon a body part.
• Researchers have suggested that excessive use of a pinch gripping is
the greatest contributing risk factor in the development of MSDs
among dental practitioners (Sanders, 1997)
• The risk of developing an MSD increases when same or similar parts
of the body are used continuously, with few breaks or chances for
• Highly repetitive tasks like endodontic procedures can lead to fatigue,
tissue damage, discomfort and eventually injury.
• The wrist is in constant demand, often
sustaining excessive and repeated stresses and
• The safest position for the wrist is a straight or
neutral position. Special care should be used to
avoid bending the wrist downwards (flexion) or
outwards (ulnar deviation).
The following diagram shows the reduction in strength which occurs as
the wrist deviates further away from its neutral posture.
Carpal Tunnel Syndrome (CTS)
• CTS occurs when the median
nerve, which runs from the
forearm into the hand,becomes
pressed or squeezed at the wrist.
• The median nerve controls
sensations to the palm side of the
thumb and fingers (although not
the little finger), as well as
impulses to some small muscles in
the hand that allow the fingers and
thumb to move.
• Researchers have highlighted that one of the predictors for the high
prevalence of CTS among dentists was their longer clinical period of
repetitive movements when work was done on parts of the mouth
that were difficult to access and required precise movement and
control (Mangharam, 1998)
Tendonitis of the Wrist
• Tendonitis is an inflammation of tendons, which are the structures
that attach muscle to bone.
• Tendonitis of the wrist is accompanied by pain, swelling and
inflammation on the thumb side of the wrist, and is made worse with
grasping and twisting activities .
• People with this disorder have often noted an occasional “catching”
or snapping when moving their thumb.
• Guyon's canal is a space at the wrist between the piriform bone
and the hamate bone through which the ulnar artery and the
ulnar nerve travel into the hand.
• Compression of ulnar nerve occurs in this space at the base of
the palm. It is commonly caused by repetitive wrist flexing or
excessive pressure on palm.
• It is characterized by pain, weakness,numbness, tingling &
burning in the little finger and part of the ring finger.
• This disorder is characterized by pain and swelling in the thumb and
wrist area when grasping, pinching, twisting, and a decreased range
of motion of thumb with pain.
• Possible causes include synovial sheath swelling, thickening of
tendons at base of thumb, and repeated trauma or twisting
• Trigger Finger often results from sustained forceful grips and
repetitive motion which irritates the tendon and tendon sheath
• Nodules form in tendon causing warmth, swelling, and tenderness of
• The fingers lock in the “Trigger Position”.
• The elbow should generally be held at a right
angle or ninety degrees.
• Because blood vessels and nerves supplying
the forearm and hand travel along the elbow
joint, repeated or prolonged bending can cause
compression, leading to forearm and hand
• The forearm flexors, attach at the inside portion of
the elbow. Whereas the forearm extensors, used to
open the hand, attach at the outside of the elbow.
• Injuries at the elbow typically occur at either the
inside of the elbow, referred to as Medial
Epicondylitis (golfer’s elbow), or outside of the
elbow, known as Lateral Epicondylitis (tennis elbow).
Cubital Tunnel Syndrome
• Cubital Tunnel Syndrome is often caused by prolonged use of the
elbow while flexed, resting the elbow on an armrest, or trauma from
overuse can compress the ulnar nerve.
• It is characterized by pain, numbness, tingling and impaired sensation
in the little and ring fingers, side and back of hand, loss of fine
control,and reduced grip strength.
• Rounding the shoulders can compress nerves, arteries, and veins that
supply the arm and hand, leading to upper extremity symptoms.
• Poor thoracic alignment also limits oxygen intake.
• Slouching forward compresses the chest cavity,preventing the
diaphragm muscle from completely filling the lungs with air.
• When oxygen is diminished, the body experiences fatigue and loss of
• The term bursitis means that the part of the shoulder called the bursa
• There are many different problems that can lead to symptoms from
inflammation of the bursa, one of those being impingement.
Thoracic Outlet Syndrome (TOS)
• TOS is a condition resulting from compression of the nerves, arteries,
and veins as they pass through from the neck to the arm (thoracic
• Possible causes include tight scalenes and pectoralis muscles, extra
cervical rib, and prolonged durations of working with elevated elbows
• This disorder is characterized by pain in the neck, shoulder, arm or
hand, numbness and tingling of fingers, muscle weakness/fatigue,
and cold sensation in the arm, hand or fingers.
Rotator Cuff Tear
• The rotator cuff (RC) is a group of 4 muscles;
supraspinatus, infraspinatus, teres minor and
• The RC assists with both gross and fine motor control
of the arm.
• RC injury tends to occur where the muscle’s tendon
attaches to the bone.
• Pain and discomfort are the most common complaints reported in the
neck/shoulder region amongst dental professionals.
• Studies have also shown that female dentists reported neck
symptoms 1.4 times more often than male dentists (Mangharam,
• The slight inward curve of the neck balances the head on the spine.
• Holding the head forward disturbs this balance, straining the joints
and the muscles of the neck and upper back.
• This posture also causes compression of the nerves and blood vessels
as they exit the neck, leading to symptoms in the arm and hand.
Myofascial Pain Disorder (MPD)
• MPD is characterized by pain and tenderness in the neck, shoulder,
arm muscles, and a restricted range of motion.
• Possible causes include overloaded neck/shoulder muscles.
• This disorder is characterized by intermittent/chronic neck and
shoulder pain or
• stiffness, headaches, hand and arm pain, numbness, tingling, and
• Possible causes include age-related spinal disc degeneration leading
to nerve compression and spinal cord damage, arthritis, and time
spent with the neck in sustained awkward postures.
• The main risk factors associated with dental work are the sustained
awkward postures and poor seating.
• Most individuals with low back pain do not simply injure their back in
one incident but rather gradually over time.
• Repeated stresses from over the years begin to add up and slowly
cause degeneration of various parts of the spine, resulting in low back
• In a seated posture the pressure in the lumbar discs increases by 50%
• During bending (forward flexion) and twisting (rotation) motions of
the spine, the pressure on the lumbar discs increases by 200% (Fisk,
• This type of pressure on the disc can lead to a bulge or herniation,
causing compression on a spinal nerve.
• Sciatica is characterized by pain in the lower back or hip radiating to
the buttocks and legs, causing leg weakness, numbness, or tingling.
• It is commonly caused by bulging, prolapsed or herniated discs
compressing a spinal nerve root and is worsened with prolonged
sitting or excessive bending and lifting.
Application of Ergonomics
• Through ergonomic advances made over the years, dental
professionals have been able to modify and optimize their working
• Ergonomic improvements in seating, instrumentation, magnification,
lighting, and glove use have offered a proactive measure for ensuring
a proper balance between job requirements and worker capabilities.
• Proper seating is a complex subject about which there is much
• Research findings indicate that dentists who sit 80 to 100% of the day
are at an increased risk of developing low back pain (Mangharam,
• Studies have shown that the seat moves almost every minute
throughout a typical treatment session, as the clinician is continually
adjusting their positioning to improve visual access and accommodate
• A seat should be constructed of a rigid cast frame that will not distort
with time and use.
• This rigid base must accommodate five casters to prevent rearward
tipping, however the base should not be as wide as that of an office
• The compact base ensures that the wheels do not interfere with the
feet, foot controls, or patient chair (Sanders, 1997).
• The seat pan should be wide enough to allow for some shifting and
• Twenty-five percent wider than the total breadth of the buttocks is
considered adequate for the majority of people.
• The front edge of the seat should taper off and away from the legs so
as not to impede circulation and nerve supply to the leg.
• The seat should also be height adjustable. When the feet are resting
flat on the floor the angle between the spine and the thighs should be
90 to 110 degrees.
• An angle less than 90º flattens the lumbar curve of the spine and an
angle greater than 110º gives the feeling like you are slipping off the
• Researchers recommend that a shorter clinician have a seat
adjustment range from 16 to 21 inches, while taller individuals have a
range of 21 to 26 inches.
• In an ideal situation, a clinician should be able to function from a
height range where their thighs are parallel with the floor and the
legs are in fully supported position (Sanders, 1997).
• While arm support is a controversial subject, many clinicians and
experts feel that they are essential to health and comfort.
• If elbow rests are present, they should be positioned just below
seated elbow height so that when the shoulders are not elevated
when using the rests.
• Some researchers have found the use of elbow rests to reduce upper
trapezius muscle load as well as the frequency and range of arm
abduction during regular dental tasks (Marchand,2001).
• With numerous designs currently available on the market, each chair
has its own unique advantages and disadvantages.
• As a result, it is important to speak with product specialists and try
the chair under real working conditions before committing to
• When seating a patient, optimal results will be achieved when their
oral cavity is positioned at a height equal to the seated height of the
• Positioning the oral cavity above heart level will limit vantage and
increase the rate of shoulder fatigue.
• Positioning the oral cavity below the recommended height will result
in non-neutral working postures including over declination of the
head, forward and/or lateral bending of the torso, and inability of the
clinician to access free movement in the clock positions.
• When the patient is properly positioned
your shoulders, elbows, and wrists should
be in a neutral position.
• your upper arms are close to your body
• your elbow / forearm angle is close to 90º
• your wrists are in line with the forearm
with no more than 20-30º extension
• The design of dental instrumentation can play a key role in the
prevention of negative health effects for its users.
• The goal of proper instrument selection should be to reduce force
exertion while allowing for neutral joint positioning.
Handle shape and size
• Dental instrument diameter ranges from 5.6 to 11.5 mm. Larger
handle diameters reduce hand muscle load and pinch force, although
diameters greater than 10 mm (3/8 inch) have been shown to offer
no addition advantage (Dong, 2006).
• Alternating tools with different diameter sizes allows the user to
reduce the duration of prolonged pinch gripping.
• “No. 4” handle lessens pinch gripping and can be purchased for most
• A round handle, compared to a hexagon handle will reduce muscle
force and compression.
• Lightweight instruments (15 g or less) help reduce muscle workload
and pinch force (Dong, 2006).
• The instrument should be equally balanced within the hand so that
the tendency to deviate the wrist is reduced.
• The second digit (index finger) can detect very fine movements and
should be placed close to the operating point.
• By not using the fourth digit as a stabilizer of the hand piece reduces
the number of fingers in the oral cavity, improves the ability to
position instruments, and involves as few joint segments as possible
thereby improving the degree of control and providing enhanced
Ease of operation
• The easier it is to operate a tool, the better.
• Less time is spent searching for buttons, thereby reducing the risk of
• Less time is also spent learning how to use the device. Simple
activation is also important, such as using a foot pedal or handle turn
to activate the tool as they do not require the operator to hold a
button in a sustained pinch grip for extended periods of time.
• As a tool becomes dull, additional force is required to perform tasks.
As a result, it is important to maintain sharpness of the instruments.
• Knurled handles such as diamond-shaped or crisscross patterns serve
to reduce pinch grip force due to an increase in tactile sensation as a
result of the knurl.
Additional tips for instrument selection:
• Hollow or resin handles are preferred
• Round, textured/grooves (knurled), or compressible handles are
• Colour-coding may make instrument identification easier
• Carbon steel construction (for instruments with sharp edges) is
• When selecting hand pieces, look for:
• Lightweight, balanced models (cordless preferred)
• Sufficient power
• Built-in light sources
• Angled vs. straight-shank
• Pliable, lightweight hoses (extra length adds weight)
• Easy activation
• Dental equipment should be located in a manner which allows you to
maintain a neutral working posture.
• Frequently used items should be kept within a “comfortable distance”
(22–26 inches for most people) and not above shoulder height or
below waist height.
• Frequently used items such as the syringe, hand piece, saliva ejector
and high volume evacuator should be positioned so they are within a
normal horizontal reach which is the arc created while sweeping the
forearm when the upper arm is held at the side.
• While ultrasonic tools can serve to reduce prolonged pinch gripping
they do expose the clinician to hand-arm vibration.
• While some studies indicate that prolonged use of this equipment can
be hazardous due to the negative effects associated with vibration,
other researchers suggest that its use is preferable to the heavy hand
forces experienced during manual scaling.
• The added weight of cords can often influence the level of muscle
fatigue experienced by a clinician.
• Additionally, coiled hoses can cause the hands and wrists to do more
work if the coils have too much resistance to deformation.
• it is recommended that retractable or coiled hoses be avoided and
replaced with a pliable hose which consists of a swivel mechanism in
• Newer 360 degree swivel cords also provide increased flexibility for
managing the cord. Positioning heavier cords over the arm or across
an armrest can also be beneficial for reducing muscle strain (UBC,
• Mouth mirrors have been referred to as the most important, yet
underutilized instruments within dental practice. Good mirrors
coupled with proper use can significantly increase one’s opportunity
to maintain a neutral working posture.
• It is important to remember that a mirror should be held lightly and
lowered into the mouth with the handle held no more than 45
degrees from the vertical plane (University of British Columbia (UBC,
• If static retraction is required, it is recommended that a proper
retraction tool be used, such as those commonly used in oral surgery
practices (UBC, 2008).
Working Posture and Techniques
• A neutral working posture is defined as one which supports
uncompromised musculoskeletal balance of the clinician.
• most clinicians attempt to use a wide range of positions around the
patient’s head, often referred to as the “o’clock positions”.
• For right-handed clinicians, working in the range from 7 to 9 o’clock is
commonly associated with twisting of the trunk and neck as well as
working with an elevated elbow posture in order to gain access.
• The mirror image (3 to 5 o’clock) is equally problematic for left-
handed clinicians. In an attempt to reduce such postural deviations a
conservative range from 10 o’clock to approximately 12:30 is
preferred and shown below (UBC, 2008).
• More recently, discussion has shifted towards the use of a “biocentric
• Which shifts the work load from the small muscles of the hand and
forearm to the larger muscle groups of the upper arm and shoulder.
• Using this technique allows the clinician to
• maintain a neutral upper extremity position (shoulders level, upper
arm vertical,and forearm horizontal) while still offering options for
accommodating patients'anatomical variations.
• Researchers believe the biocentric technique reduces muscular
fatigue by varying task performance (Meador, 1997).
• The use of 2-finger rests has shown musculoskeletal advantages when
performing scaling procedures. When researchers examined three
different finger positions (no rest, 1-finger rest, and 2-finger rests)
they found significant reductions in thumb pinch forces and muscle
activity when using rests.
• As a general rule, the greater the force applied during a task, the
greater the requirement for hand stability.
• Through the use of finger rests, dental practitioners can increase
stability while also reducing muscular loading. The closer one can
position their finger rest to the target area, the greater the level of
micro-control will be achieved.
• Modifying one’s work schedule has been suggested as an effective
preventive measure for providing sufficient recovery time and
avoiding muscular fatigue.
• Recommendations when scheduling include:
• • Incorporate brief “stretch break” periods between patients
• • Develop a patient difficulty rating scale to ensure difficult treatment
• sessions are not performed consecutively
• • Increase treatment time for more difficult patients
• • Alternate heavy and light calculus patients throughout the day
• • Alternate procedures performed throughout the day
• • Shorten patient’s recall interval
• The majority of people prefer the use of their dominant hand when
performing manual operations. While this can improve efficiency, it
can also result in muscular overload of the dominant hand/arm.
• It is recommended that individuals attempt to alternate hands
throughout the workday, whenever possible.
• Although this may not be practical for certain precision tasks, it is
possible to alternate hands when performing accessory tasks, such as
reaching for tools or supplies.
• Frequent stretch breaks can prevent detrimental physiological
changes that can develop while working in static or awkward
• In an attempt to prevent injury from occurring to muscles and other
tissues, dental professionals should allow for rest periods to replenish
and nourish stressed structures. If breaks are
• too far apart, the rate of damage could exceed the rate of repair and
• lead to the breakdown of tissue.
• Researchers suggest that dental professionals try to
• lean back in their stool at least four times during each treatment
session as well
• as spend three to five minutes stretching for every patient seen
• day (Sanders, 1997).
• Points to Remember:
• • Perform a variety of stretches throughout the workday
• • Stretching should be gentle and gradual
• • Do not stretch a muscle to the point of pain
• • Stretches can be held up to 10 seconds and repeat 3-5 times
• • Breathe normally while stretching
• • If you suffer from a musculoskeletal condition consult a Physician
• attempting new exercises which you are unfamiliar with